WO2011113119A1

WO2011113119A1 - Process for the treatment of cellulose pulps, cellulose pulp thus obtained and use of biopolymer for treating cellulose pulps

Info

Publication number: WO2011113119A1
Application number: PCT/BR2010/000081
Authority: WO
Inventors: Romolo Ranocchia; Ademilson Massoquete
Original assignee: Fibria Celulose S/A
Priority date: 2010-03-19
Filing date: 2010-03-19
Publication date: 2011-09-22
Also published as: BR112012024018A8; CN103109014B; NZ602846A; BR112012024018A2; PT2547823T; US20150315750A1; AU2011229082A1; US20130228297A1; CN103109014A; CL2012002576A1; US11047092B2; US20180073197A1; CA2793557A1; PL2547823T3; US9828728B2; WO2011113126A2; EP2547823A2; US9096974B2; US20170204566A9; ES2595249T3

Abstract

The present invention relates to an improved process for producing chemical cellulose pulp wherein biopolymers are added immediately before, during or after a bleaching step, depending on pulp characteristics and on process conditions used. The biopolymers according to the present invention are starch by an etherification reaction. This treatment results in a differentiated pulp having improved physical, chemical and mechanical properties when compared with cellulose pulps obtained by traditional processes. The use of said biopolymer alters the relations between important pulp properties rendering their application in papermaking process advantageous. This differentiation increases the possibilities of use and also of new applications, including for the substitution of pulps produced from other cellulose sources.

Description

Title: "PROCESS FOR THE TREATMENT OF CELLULOSE PULPS, CELLULOSE PULP THUS OBTAINED AND USE OF BIOPOLYMER FOR TREATING CELLULOSE PULPS".

Field of the Invention

The present invention relates to a process for the treatment of cellulose pulps for enhancing said bleached pulps quality and applicability, especially their mechanical strength and drainability properties, by incorporating - biopolymers specifically developed as additive into producing process recipe of said differentiated cellulose pulp.

Background of the Invention

In addition to forest developments and treatments directed to paper manufacturing process for developing mechanical strength and other equally important properties, in the last few years, researchers of the sector have been working on additives association as the most promising means to enhance these properties in cellulose manufacturing process itself. Among the additives that have been used for manufacturing paper are the longer fibers, glues_^, dry and wet strength agents, starch, and others.

Document WO 00/28141 describes a method for treating lignocel- lulosic fibrous materials for enhancing the mechanical strength and humidity properties of the final product, which comprises fibrous materials, in which paper is the major example. The treatment involves the application of lignin derivatives in a solvent system with secondary additives which consist of a broad scope of sugars and natural polymers. This document describes the addition of additives in the paper machine approach flow, in the so-called wet end of the paper machine, where most additives are included in paperma- king. Some additives mentioned in that patent application are widely known by the properties they provide when used in the recipe for producing some types (grades) of papers. In addition, the process described in that document requires the combination of the use of lignin for obtaining the desired results, which actually corresponds to the innovative aspect of that invention, and other secondary natural polymers are included as optional for boosting the development of the desired properties. Another document describing the use of (the) biopolymer starch in a process for producing cellulose is PI9803764, which relates to a method for bleaching cellulose pulp with whitening chemical substances with the addition of starch, polyvinyl alcohols or enzymes. This document specifies the treatment for pulps having more than 5% lignin, emphasizing higher yield pulps such as mechanical pulps, thermomechanical pulps and chemother- momechanical pulps; thus, pulps without an ostensive bleaching process such as that of chemical pulps. The object of that invention is only to increase the whiteness of the pulp, and the secondary additives, such as enzymes and starch, are only intended to increase the efficacy of the optical whitening agents thus enhancing their absorption on the surface of the treated pulp fibers. These products for enhancing pulp whiteness are added in the last step before drying the pulp and do not develop the mechanical properties of the pulp.

Accordingly, the object of the present invention is the use of a biopolymer in a process for cellulose pulp treatment that is capable promoting changes in the mechanical properties as well as in other important properties, such as drainage, porosity and pulp refining.

Summary of the Invention

In a first embodiment, the present invention relates to a process for treating acid or alkaline cellulose pulps comprising a step of adding at least one biopolymer during the preparation process of said pulps, wherein the biopolymer is a starch modified by an etherification reaction.

In a second embodiment, the present invention relates to a cellu- lose pulp obtained by a process of treatment with at least one biopolymer, which is a starch modified by an etherification reaction.

The present invention further relates to the use of a biopolymer starch modified by a chemical reaction of etherification that enables the link between polymeric chains and some that underwent a reduction in the poly- meric chain by hydrolysis reaction for the treatment of acid or alkaline cellulose pulps.

Brief Description of Drawings Figure 1 shows a graph with data about the effect of adding a bio- polymer according to the present invention to an alkaline pulp in the relation between tensile index and bulk considering refining effect in a PFI mill.

Figure 2 shows a graph with data about the effect of adding a bio- polymer according to the present invention to an alkaline pulp in the relation between the tensile index and the Schopper Riegler value (^eSR) considering refining effect in a PFI mill.

Figure 3 shows a graph with data about the effect of adding a bio- polymer according to the present invention to an alkaline pulp in the relation between the tensile index and the Gurley value, considering refining effect in a PFI mill.

Figure 4 shows a graph with data about the effect of adding a bio- polymer according to the present invention to an acid pulp in the relation between the tensile index and bulk considering refining effect in a PFI mill.

Figure 5 shows a graph with data about the effect of adding a bio- polymer according to the present invention to an acid pulp in the relation between the tensile index and the Schopper Riegler value considering refining effect in a PFI mill.

Figure 6 shows a graph with data about the effect of adding a bio- polymer according to the present invention to an acid pulp in the relation between the tensile index and the Gurley value considering refining effect in a PFI mill.

Figures 7 and 8 show a graph with data about the effect of adding a biopolymer according to the present invention to alkaline and acid pulps, respectively, in the relation between the tensile index and energy consumption considering refine effect in a pilot plant.

Figure 9 shows a graph with data about the effect of adding a biopolymer according to the present invention to an alkaline pulp in the relation between the tensile index and bulk considering refine effect in a pilot plant.

Figure 10 shows a graph with data about the effect of adding a biopolymer according to the present invention to an alkaline pulp in the relation between the tensile index and the Schopper Riegler value considering refine effect in a pilot plant.

Figure 11 shows a graph with data about the effect of adding a bi- opolymer according to the present invention to an alkaline pulp in the relation between the tensile index and the Gurley value considering refine effect in a pilot plant.

Figure 12 shows a graph with data about the effect of adding a bi- opolymer according to the present invention to an acid pulp in the relation between the tensile index and bulk considering refine effect in a pilot plant.

Figure 13 shows a graph with data about the effect of adding a bi- opolymer according to the present invention to an acid pulp in the relation between the tensile index and the Schopper Riegler Value considering refine effect in a pilot plant.

Figure 14 shows a graph with data about the effect of adding a bi- opolymer according to the present invention to an acid pulp in the relation between the tensile index and the Gurley value considering refine effect in a pilot plant.

Detailed Description of the Invention

The biopolymer developed for the present invention is a polymer of natural origin which is submitted to a chemical reaction of etherification. More specifically, it is a modified starch in such a way that the hydrogen a- tom of molecule reactive group is substituted with another radical: 2,3- epoxypropyl-N-alkyl-N,N dimethylammonium chloride. The biopolymer can be produced from corn starch, manioc starch or any other plant source of starch.

Preferably, the etherification reaction for modifying the natural starch is carried out in an alkaline medium, in aqueous suspension with a solid content of 20% to 65% and under a controlled temperature conditions between 20° to 50°C during a period of about 8 to 16 hours. In this reaction medium and using an alkaline catalyst to promote oxydryl groups activation, the process renders the starch molecule susceptible to the substitution reaction with an epoxide reactive agent (2,3-epoxypropyl-N-alkyl- N.Ndimethylammonium chloride) from (3-chloro-2-hydroxypropyl- trimethylammonium) amide with the stoichiometric addition of an alkali.

The abovementioned chemical modification was verified in bio- polymers with different charges, comprising positive, negative, neutral or mixed charges wherein a same biopolymer chain has at least two types of diffe- rent charges and can be characterized by the Degree of Substitution (DS). This value is determined by the average number, expressed in molar basis, of hydroxyl groups substituents of each D-glucopyranosyl unit that is part of the biopolymer. Several biopolymers were assessed with the DS of the set varying within a range of 0.020 to 0.065.

This modification process confers special characteristics to the biopolymers which favor their interaction with the fibers and other cellulose pulp components, such as vessels and fines elements. As a resulting benefit from this higher interaction there is an increase in bonds amount between the biopolymers and the several fractions of cellulose pulps. As a conse- quence of this procedure, it is possible to obtain an increase in cellulose physical resistance and draining proprieties.

Biopolymers act on cellulose with the formation of hydrogen bonds by multiplying the bonds among the fibers and helping to retain fines, which improves the mechanical strength and drainage of the paper produced in the future. Hydrogen bonds are ionic and considered to be weak; yet, they represent a significant contribution to cellulose and paper properties. Among them, the biopolymer molecules can form bonds with the creation of crystalline regions having high binding capacity between fibers and fines, uniformly forming high resistance clusters distributed in cellulose and in paper. The intensity of this phenomenon may vary with specific biopolymers constitution, size distribution and molecule dispersion, in addition to chemical modifications promoted by other reactions.

Other interactions can be present in the contacts between the biopolymers of the present invention and cellulose and paper components such as electrostatic attraction and Van der Waals forces. This diversity of biopolymer interactions ensures its permanent effects on paper final characteristics even after going through cellulose and paper manufacturing process. The modified biopolymers used in the present invention are selected according to each type of cellulose pulp to be treated and, therefore, according to each type of specific production process, depending on reaction conditions and on the degrees of substitution required for the desired results.

The inventors have noticed that the addition of these biopolymers specifically developed for the process of the present invention can differentiate pulps properties, particularly cellulose pulps of eucalyptus, with a substantial increase in tensile strength, tear resistance, drainability, air permeability, among other important and desired properties. This enables differentia- ted and innovative applications, and the possibility of using more short fibers instead of the long fibers, and can result in improvements in plant productivity or energy savings because it facilitates pulp dewatering in the drying stage.

As the properties of cellulose treated according to the process of the present invention are in-between the short- and long-fiber celluloses, with some important relations among those properties being better than those of the original eucalyptus fiber cellulose, the differentiated cellulose thus obtained can also be considered a new long-fiber substitution product. Due to the differences obtained for the biopolymer used in the present invention, they can be employed in pulps applied in the manufacture of different types of papers, such as printing, writing, decovative, special or tissue-type papers, for instance.

It is also well-known that the biopolymers adsorbed in the cellulose fibers can go through a disintegration, refining and depuration process, when cellulose later enters the paper manufacturing process. The biopoly- mers still retain the special characteristics obtained in the process of cellulose manufacturing enabling savings in some additives that are typical of certain kinds of papers that can be reduced or eliminated.

According to pulp manufacturing process and to the present in- vention, the addition of the biopolymer can be made in several ways and in at different times in view of the process variables which, in turn, vary in view of pulp desired characteristics. Some of these conditions can be obtained in delignification stage with oxygen, between the bleaching stages or even right after the pulp is bleached.

The process according to the present invention can also be applied to high yield pulps, which are pulps that do not go through a more drastic cooking and bleaching process, such as the chemical pulps, and keep their yield above 65%, provided they meet the biopolymer application conditions. Among the most well-known high yield pulps, mechanical, thermomechanical and chemothermomechanical pulps can be mentioned.

After going through the bleaching process, an additional treatment can be applied to the cellulose pulp under the required conditions for the biopolymer to modify said pulp. The biopolymer added in this stage, that is, after bleaching, should be activated by a cooking process, under conditions to be determined according to the specific characteristics of the biopolymer used. In the case of biopolymers that accept alkaline conditions, for exam- pie, they can be added in suitable temperature, pH and residence time conditions, in several points of the process, such as: oxygen delignification and alkaline stages of bleaching. In both cases, the biopolymers are fixed to the pulp before it is sent to the paper production process, going through the obtained cellulose drying, baling and rebeating processes without losing the characteristics added.

According to a preferred embodiment of the invention, the process for treating the cellulose pulp comprises a process of bleaching alkaline pulp having the sequence ADo(Eop)PP wherein the acronyms of the bleaching stages mean: A, the acid stage; Do, the short stage of chlorine dioxide; Eop, the alkaline extraction stage with small oxygen and hydrogen peroxide doses and P, the hydrogen peroxide dosage stages and wherein the biopolymer is added between one of the alkaline steps of bleaching or in an alkaline step before bleaching.

Still in a preferred embodiment, the biopolymer is added to the cellulose pulp during the treatment process in an amount of 5,0 kg/tsa to 20.0 kg/tsa based on pulp total amount, in a temperature range of from 45°C to 95-C, preferably from 70 to 90⁹C, and with a contact time between the bi- opolymer and the pulp in the range of 10 min to 360 minutes, preferably from 30 to 90 minutes. Preferably, the pH during the addition of the biopolymer is from 8 to 11 for alkaline pulps and from 3 to 6 for acid pulps.

Behavior assessments of- regular variations in the cellulose mariu- facturing process relating to the properties of the cellulose modified with bio- polymers according to the present invention should be made for each production process. In addition, an assessment of the interference of this new modified cellulose product in the properties and in the manufacturing process of different types of papers should be carefully developed for the application of cellulose modified with biopolymers, and such parameters may be promptly determined by skilled artisans and do not represent an essential and determinant characteristic of the present invention.

Examples

The following examples will better illustrate the present invention, and the particular conditions and parameters described represent preferred, and non-limiting, embodiments of the present invention.

Example 1

For a alkaline pulp treating process, it was used a biopolymer herein identified as "AlcBiol", referring to a hybrid corn polysaccharide chemi- cally modified by etherification in the following conditions: pH of 8.5 in aqueous suspension with 30% of solids concentration and a controlled temperature of 30°C, during a period of 8 hours. Its physical aspect corresponds to a fine white powder having a characteristic starch odor, insoluble in water and organic solvents. With regard to its chemical characterization, said biopoly- mer AlcBiol has a degree of substitution of 0.025 to 0.045, hydrogenionic potential (pH) of 5.5 to 6.5 and maximum humidity of 14%.

Example 2

For alkaline pulp treating process, it was used a biopolymer herein identified as "AlcBio2", referring to a corn polysaccharide chemically modified by etherification in the following conditions: pH of 8.5 in aqueous suspension with 40% solids concentration and a controlled temperature of 40°C, during a period of 6 hours. Its physical aspect corresponds to a fine, white powder, insoluble in water and organic solvents. With regard to its chemical characterization, said biopolymer AlcBio2 has an amphoteric charge (positive and negative) with a degree of substitution of 0.025 to 0.042, hydrogenionic potential (pH) of 5;5 to 6.5 and maximum humidity of 14%.

Example 3

For alkaline pulp treating process, it was used a biopolymer herein identified as "AlcBio3", referring to a corn polysaccharide chemically modified by etherification in the following conditions: pH of 9.0,. in aqueous suspension with 35% of solids concentration and a controlled temperature of 30°C, du- ring a period of 8 hours. Its physical aspect corresponds to a fine white powder, insoluble in water and organic solvents. With regard to its chemical characterization, said biopolymer AlcBio3 has anionic charge, hydrogenionic potential (pH) of 5.5 to 6.5 and maximum humidity of 14%.

Example 4

For acid pulp treating process, because of process conditions requirements, the boiopolymer herein identified as "AcBio2" was used, which is an aqueous solution formed by a starch polysaccharide chemically modified as previously described having the degree of substitution in the range of from 0.022 to 0.040, pH of 5.0 to 6.0, and containing preservative based on ben- zisothiazolinone. This preservative was needed to avoid degradation of the product, which is quite susceptible to attacks of microorganisms. Biopolymer AcBio2 has the following physical features: cream color viscous solution, characteristic odor of starch, maximum bulk density of 1.13 g/cm³, solid contents of 24.0% to 27.5%, maximum viscosity of 2000 cP, and hydrogenionic potential (pH) of 5.5 to 7.5.

Comparative Test Results

With these examples of biopo!ymers AlcBiol (alkaline process) and AcBio2 (acid process), laboratory tests, intermediate and industrial scale tests were carried out. The results obtained in these cases show important developments on modified cellulose properties. In laboratory scale, the e- quipment used was a cellulose bleaching reactor with a 300g dry fibers ca- ^" pacity, and total automatic control of the process conditions. In the pre- industrial scale test of the process, the reactor used, which had a.100 kg dry pulp capacity, also had automatic control of the process variables. However, in this case, the addition and shearing conditions were closer to the industrial conditions due to pumping operations and loss of load during cellulose transportation.

Optimized procedures with alkaline pH pulp were developed to use the biopolymer without interfering in the cellulose manufacturing process. To this end, the biopolymer was added between the two stages of hydrogen peroxide, within the sequence used for cellulose bleaching. In this stage, the bleaching conditions, which were compatible for the application of the biopolymer, were: pH - 11.0, temperature - 90°C, consistency - 10% and retention time - 80 minutes. For these conditions, biopolymer AlcBiol was chosen. This biopolymer was dosed in several quantities relating to the percentage of dry fiber with a view to optimizing its dosage.

Biopolymer application to alkaline cellulose was done in-between the bleaching stages, because these technical conditions were the most advantageous for activating their desired contributions. However, other alkaline stages can also receive said biopolymers dosage with equally advantageous results with regard to the base pulp.

Other studies in larger scale were also carried out, including assessing the refining capacity of the resulting pulp so as to confirm the advantages obtained with the present procedure. As expected, the results were proportionally increased in relation to the dosed quantities. However, as the dosage effect is not linear, a cost/benefit analysis shows that the dosage can be optimized with the use of this process in industrial scale, but it is currently around 0.5 to 1.5%. Part of the results shown later in this document relate to 1.5% dosages of the biopolymer AlcBiol in these conditions.

Cellulose modification development with biopolymers was complemented in a second step with the modification of the acid pulp, as indica- ted in example 2. The purpose of this study was to improve the development of a biopolymer suitable for the many acid pH conditions noticed in cellulose producing process. This dosage required other biopolymers types, since the process conditions are different and incompatible with the biopolymers used in the previous process, which is alkaline. The biopolymers that will be added to cellulose in acid pH should be activated out of the cellulose production process, before their addition. In this case, the biopolymer AcBio2 was obtained and is suitable for cellulose producing process with application in the pulp in the end of the bleaching process. Said biopolymer AcBio2 was applied in the following conditions: pH - 5.5; temperature - 70°C; consistency - 10% and retention time - 30 minutes. The biopolymer dosage is similar to the described in alkaline pulps, and the results are also as satisfactory as those achieved with these pulps. This condition can be facilitated if the last stage of bleaching is acid. In this case, an effective mixture with the pulp significantly contributes to the effect of the biopolymer before a probable dilution of ceikflose in later operations process.

The studies carried out with the biopolymers of the present inven- tion show that, although the results are not linear, the properties gain is directly proportional to the additive amount added, which advantageously can be from 5.0 kg/tsa to 20.0 kg/tsa. From the samples selected for the pilot test, one was applied in the alkaline condition and the other in the acid condition according to the possible success rates for working with these biopoly- mers within the cellulose manufacturing process.

The initial experimental work of the present invention included laboratory tests for sole application in pulps produced in alkaline pH because the process condtitions for such cellulose seemed to be the most suitable for the required development. Actually, after multiple tests and modifications to the biopolymers, the results were positve in these conditions. After these first results, biopolymers development for use in pulps with acid pH was less expensive and the resuls obtained were equally positive.

After defining process conditions, the product dosages were also optimized. Although the amount added is also linked with development sca- le, as seen in the test carried out in the pilot plant. The tests made in the pilot plant, in the conditions used in the laboratory, but in reactor with a 100 kg dry pulp capacity, showed the same improvement tendency of interest properties. The biopolymer in this case should be diluted in potable water or in wash water of the bleaching stages with maximum distribuition and mixing with the pulp that receives it.

Both cases tested enhanced the mechanical strength and draina- ge properties in spite of the different characteristics of the biopolymers applied. Despite the costs involved with the biopolymers added in this invention, compensation was detected in pulp refining for paper production when this operation is obviously required. Refining shows that for this differentiated pulp with a biopolymer the required energy to arrive the same drainability degree and mechanical strength is lower than that needed for the pulp with the same fiber without the presence of biopolymer, in all process conditions tested. Obviously, this advantage should vary according to the refining technology used and paper type where this cellulose is applied.

First of all, some important results are presented for alkaline pulps obtained in laboratory scale.

The results shown in Figure 1 demonstrate the relation between the tensile index, as the first property to be developed as reference, that is, the purpose was to increase the mechanical strength of the pulp also providing a positive relation with other important properties. Biopolymer addition according to the invention shows that there is an increase in the tensile s- trength and bulk within the ^"studied grinding curve; for the same bulk the increase in the tensile index is very significant, and vice-versa.

The amount of biopolymer AlcBiol added in the experiment was 1.5% biopolymer over the dry mass of the substrate to be treated.

The relation between the tensile index and the Schopper Riegler value (⁹SR) (a measurement of the rate at which a diluted pulp suspension may be de-watered) shown in Figure 2 demonstrates that, with the use of biopolymer AlcBiol , a pulp with higher mechanical strength and lower energy cost was obtained for drying the same amount of pulp or an increasing the production of the plant with the same energy consumption.

Other parameter measured was the relation between the tensile index and the Gurley value (measure of how fast a defined volume of air can pass through a defined area of membrane at standard pressure), which characterizes the air permeability of the cellulose pulp sheet. The results are shown in Figure 3. This property is especially interesting due to its development during. the process of grinding, in the PFI laboratory mill. The increase in air permeability can also imply an improvement in the drying process, especially in the paper machine where cellulose has gone through the refining process.

In the case of acid cellulose, similar analyzes were carried out u- sing the knowledge acquired in the previous case. For this study, biopolymer AcBio 2 was used with the specificaiton of the degree of substitution 0.022 to 0.040 and pH of 5.0 to 6.0. The biopolymer amount added in the experiment was 1.5% biopolymer over the dry mass of the substrate to be treated.

As can be observed by the results, the gains in all properties were similar, considering the large difference between the biopolymers and the dosage points among the pulps being studied. The relation between the tensile index and bulk shows an increase in the tensile index and bulk in the entire grinding range studied in the laboratory experiments. In the case of acid pulps, it is evident that the tensile gain for the pulps with biopolymers is higher than that with the original pulps (white), for the same amount of e- nergy applied (Figure 4).

The relations between the tensile index and the Schopper Riegler value (°SR) for the acid pulps with and without biopolymer shown in Figure 5 are higher than the results for the alkaline pulps. However, this benefit is very important in alkaline pulps because of their higher greater draining diffi- culty.

Figure 6 shows a decrease in air resistance with the application of biopolymer for the acid pulp.

These were the properties with the highest interest among those investigated, which show the invention efficacy in developming important properties that are constantly requested by customers of short-fiber cellulose. Other properties such as tear and opacity also show advantages with the application of biopolymers according to the present invention. To confirm the values obtained on laboratory scale, a pilot test was conducted in a plant with a 100 kg pulp capacity, considering air-dried fibers. The pilot plant, in which the cellulose treated with biopolymers produced according to the process, of the invention, consists of a dilution tank, wherein the pulp was prepared under the required conditions and a mixer that receives the required reagents. In this case, the reagents and the process conditions were similar to those used in the laboratory. The reagent is only the biopolymer added to the pulp at 10% consistency and the process conditions were exactly the same with a residence time of 60 minutes, tem- perature of 60°C and reactor rotation of about 28 rpm.

After going through the mixer, the pulp enters the reactor where the reaction conditions and the retention time were preserved. After the reactor, the pulp went through a discharge tank and a dewatering table that enabled the pulp to reach up to 35% dryness. Drying was concluded in a drying room under controlled temperature and humidity conditions so that the pulp properties were not affected by hornification other than by traditional cellulose drying.

The obtained pulps were refined in pilot plant refiners with 12-inch diameter disks. The disks employed enabled the use of a very low intensity refining technology, which is proper for eucalyptus cellulose. The results of such refining show substantial energy savings for pulps with biopolymers of the present invention compared with common eucalyptus pulps, using as basis the same mechanical strength expressed in the cellulose tensile index, as can be seen in the drawings.

The drawings refer to alkaline and acid pulps which are refined in the papermaking process, which in both cases represent energy gains for the paper manufacturer with biopolymer use. The drawings also clearly indicate that energy amounts applied during refiining in pilot plants, which should be related with properties magnitude shown in the sequence.

Figure 7 compares a reference pulp with another pulp with the application of 1.0% biopolymer AlcBiol and the same energy was used for both pulps. The comparison of theses pulps shows that energy can be saved to obtain the same mechanical strength through refining.

Under similar comparison conditions, figure 8 shows the refining results in a pilot plant for acid pulps. The properties analyzed in the sequence refer to the pulps obtained and refined in a pilot plant, therefore submitted to different treatments and stresses than the pulps obtained and treated in the laboratory scale. The results obtained also corroborate the results on laboratory scale . showing the same gain tendency of the same properties a- nalyzed. In this case, there is also an improvement in the mechanical s- trength and drainage propertites, which are two characteristics that potentia- te the application of this modified cellulose.

Figure 9 shows a small bulk gain with the addition of 1.0% bio- polymer in alkaline pulp, the results in the industrial application should be similar to these results or even better due to better process conditions. The increasing bulk effect is always advantageous for cellulose.

The drainability effect for the alkaline pulp shown in Figure 10 also followed a positive tendency reiterating the results on laboratory scale.

Figure 11 shows the positive effect achieved with biopolymer application of the present invention in air permeability increase of cellulose, which grows as the refining effects intensify.

In the case of acid pulp, the tendency is also to have a bulk increase with biopolymer presence throughout the refining curve in the pilot plant. This result is coherent with alkaline pulp effects, and the results on laboratory scale show that these gains can be better (Figure 12).

Figure 13 shows the gain in Schopper Riegler value during the development of refining in a pilot plant. This represents a property gain with lower energy consumption or even a possible increase in the productivity of the cellulose drying machine and the paper machine, with the same mechanical strength properties.

Figure 14 shows the refining curves for the Gurley valeu, following the same tendency of the alkaline celluose and of the laboratory scale tests, shows a decreasing in air permeability resistance, which is measured with the Gurley equipment, as a biopolymer contribution. This advantage increa- ses with refining development.

All the presented results are evidence of cellulose properties modifications and, more than that, they show that the interrelationships among important properties are posivivelly changed bringing greater benefits to cel- lulose application. These modifications result in the possibility of having intermediate applications in-between the properties of short- and long-fiber celluloses having a great substitution potential with percentage advantages of the long fibers in the paper recipes, specially in tissue paper and in printing and writing papers.

Claims

1. A process for the treatment of cellulose pulps comprising a step of adding at least one biopolymer during the process of preparation and treatment of said pulps, characterized in that said biopolymer is starch modified by the chemical reaction of etherification.

2. A process, according to claim 1 , characterized in that said biopolymer is corn starch.

3. A process, according to any one of claims 1 to 2, characterized in that said biopolymer is added in an amount of 5.0 kg/tsa to 20.0 kg/tsa in relation to the total amount of pulp.

4. A process, according to any one of claims 1 to 3, characterized by being an alkaline pulp bleaching process comprising the sequence A- Do(Eop)PP and the biopolymer is added between the alkaline bleaching steps or in an alkaline step before bleaching.

5. A process, according to any one of claims 1 to 3, characterized in that it is an acid pulp bleaching process and that the biopolymer is added during the bleaching stage or after this stage.

6. A process, according to any one of claims 1 to 5, characterized in that the biopolymer is added approximately at 45°C to 95^SC with a contact time between the biopolymer and the pulp in the range of from 0 to 360 minutes.

7. A cellulose pulp, characterized by being treated by a process, as defined in any one of claims 1 to 6.

8. Use of a starch modified by a chemical reaction of etherificati- on, characterized by being in the treatment of cellulose pulps.